1. Field of the Invention
This invention relates to a processing system having an improved mechanism for transferring objects such as semiconductor wafers.
2. Description of the Related Art
FIG. 3 shows an example of an ion injecting apparatus in which ions generated by an ion generator I in a terminal unit T are turned by an analysis magnet M and pass through an accelerating tube A. Then, the ions are successively injected into a plurality of wafers W placed on a turn table 1a (which is positioned vertically during an ion injection process) located in a process chamber 1.
The wafers, which are supplied from an external device, must be placed at exactly the right positions on the turn table 1a. For example, as shown in FIG. 4, wafers W are transferred one by one from a carrier 3 placed at a predetermined position outside the process chamber 1 by a transfer robot R1 to a positioning apparatus OD, according to conventional art. The positioning apparatus OD detects the orientation and the center of each wafer. If the orientation and/or the center is found to deviate from the correct one, the positioning apparatus OD corrects the position of the wafer by, for example, two steps: correcting the orientation and the correcting the central position. Thereafter, the wafers W are transferred from the positioning apparatus OD by the transfer robot R1 to a load lock chamber 2, a vacuum is created in the chamber 2, and the wafers are subsequently transferred therefrom to the turn table 1a by a transfer robot R2 provided in the process chamber 1.
In addition to the apparatus shown in FIG. 4, various other apparatuses and methods can be employed to batch-process wafers in a vacuum or in an atmosphere at low pressure. However, since it is difficult to transfer wafers between a vacuum and a non-vacuum state and since the unit of process (the number of wafers which can be processed at a time) differs from the unit of transfer (the number of wafers which can be held by a carrier at a time), the conventional wafer transfer apparatus has the following drawbacks:
1. It is difficult to achieve an interface between the wafer transfer apparatus and a wafer carrier distribution mechanism whereby the manufacturing process can be automated. Therefore, a special interface unit must be added, resulting in extra cost and a substantial length of time being required to correctly set up the apparatus.
2. Since a number of transfer steps are required and many of them include a wait time, wafers cannot be transferred quickly.
3. The order of transferring wafers is not suitable for keeping the main surfaces of the wafers clean. For example, if a wafer above another wafer is moved, dust may adhere to the main (upper) surface of the lower wafer.
4. Since the unit of process differs from the unit of transfer, wafer management is complicated. For example, when a processed wafer is stored in the wafer carrier, an operation of placing it back to the slot wherein the wafer is originally held is very troublesome.
5. Since wafers are transferred via a positioning apparatus, a relatively large number of transfer steps are required, thus increasing the possibility of wafer damage and/or particle contamination, and lowering the production yield. Further, the greater the number of handling steps, the longer is the transfer time, thus reducing the throughput of the apparatus.